The present invention relates a radial anisotropic ring magnet and a producing method thereof, and more particularly, relates to a ring magnet having a circumferentially formed sinusoidal waveform distribution of magnetic flux density and a producing method thereof.
An AC servomotor which can generate constant torque regardless of the rotational angle of a rotor has been required. To satisfy this requirement, it is theoretically said that a rotor-side magnet must have a sinusoidal waveform distribution of magnetic flux density along the circumference thereof.
Therefore, as a conventional method, circular blocks (eccentric segments) 100 each having its thickness changed along the circumference thereof as shown in FIG. 4 are stuck to one another in the rotor side to form a ring as a whole (in this example, four circular blocks 100 are circumferentially stuck to one another) so that a sinusoidal or substantially sinusoidal waveform distribution of magnetic flux density is provided correspondingly to the change of the thickness of the circular blocks 100.
In the case where a plurality of circular blocks 100 are stuck to one another as described above to form a ring magnet, however, the number of the circular blocks 100 must be made to correspond to the number of magnetic poles. For example, four circular blocks must be stuck to one another when the number of magnetic poles is four, and eight circular blocks must be stuck to one another when the number of magnetic poles is eight. Much labor as well as a lot of steps are required for sticking the circular blocks 100 to one another.
Further, in the case where the circular blocks 100 are stuck to one another as described above, there is a risk that the circular blocks may be separated when the motor is in use. In addition, a problem may arise on positional accuracy in sticking of the circular blocks 100.
That is, it is difficult to eliminate the shifting of the sticking positions of the circular blocks 100 perfectly. This causes cogging in the motor, that is, rotational unevenness.